Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more turbine blades. The turbine blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length of the turbine blades. However, as is generally known, the deflection of a turbine blade is a function of blade length, along with wind speed, turbine operating states and blade stiffness. Thus, longer turbine blades may be subject to increased deflection forces, particularly when a wind turbine is operating in high-speed wind conditions. These increased deflection forces not only produce fatigue on the turbine blades and other wind turbine components but may also increase the risk of the turbine blades striking the tower. A tower strike can significantly damage a turbine blade and the tower and, in some instances, can even bring down the entire wind turbine. Accordingly, a tower strike may result in considerable downtime to repair or replace damaged components.
Known wind turbine systems determine turbine blade deflection by utilizing external sensors, which are typically mounted on the turbine blades or on the tower. These sensors are designed to sense turbine blade operating conditions (e.g. blade strain, blade acceleration or blade velocity) to enable blade deflection to be inferred or calculated. However, maintaining the sensors can be very costly and calibrating such sensors can be quite complex and time consuming. Moreover, since the sensors must be calibrated frequently, there is a concern with regard to the reliability of data transmitted from the sensors over an extended period of time.
To address these issues, at least one system has been developed that utilizes a camera and two reflective targets to measure blade deflection. Specifically, the reflector targets are mounted at two different locations within the rotor blade and the camera's flash is utilized to illuminate the reflector targets as the camera captures an image. By analyzing the spatial position of the two reflectors, the blade deflection of a small portion of the rotor blade may be estimated. However, this system is only equipped to identify two reflector targets within the rotor blade. As a result, there can only be two points along the length of the rotor blade at which blade deflection can be detected, which severely limits the amount of useful data that can be acquired regarding the motion and/or shape of the rotor blade along its entire length.
Accordingly, there is a need for a system that is capable of detecting a plurality of different targets positioned within a rotor blade in order to allow for detailed data regarding the motion and/or shape of the blade to be acquired.